The present invention relates to a method of detecting a defective condition on a pressure switch assembly and to an arrangement for detecting a defective condition of a pressure switch assembly.
Pressure switches of the afore-mentioned type are mounted, for example, in automotive vehicles comprising a front axle/rear axle brake circuit division. In the event of a brake circuit failure on the front axle, they insure that a brake pressure reduction on the rear axle for adjusting the ideal brake force distribution in that case be prevented from occurring. As a rule, a pressure switch, with the brake not actuated, is closed and is opened by the brake pressure. Hence, if the pressure switch during a deceleration process, for example, with the brake light switch actuated, remains closed, this is indicative of that no pressure is built up in the front axle brake circuit. The brake circuit is defective. In order that the ECE directive requiring a 30% deceleration of the vehicle in the event of a brake circuit failure, can also be complied with by the rear axle brake circuit alone, in such an event of a detected defective condition of the front axle brake circuit, a brake force distribution is prevented by a conventional brake pressure reducer lockable by electrical means, or by cutting off a means for the electronic brake force distribution. Hence, a brake force control can be performed only with the pressure switch opened because this alone will insure that pressure is built up in the front axle. Should the pressure switch be opened only on account of a defective condition, also in a defective front axle brake circuit a brake pressure reduction would take place on the rear axle so that the required deceleration of the automotive could not be attained. For safety reasons, also other defective conditions of the pressure switch should be detected. It is the object of the invention to provide a method of the afore-mentioned type as well as an appertaining pressure switch assembly, which method enables detection of a defective condition of the pressure switch arrangement.
A method solving the afore-described problem is described by the present invention. A pressure switch arrangement generating corresponding controllable signals is also part of the present invention.
An error is recognized in the simplest way if the signal transmitted by the pressure switch arrangement to the controller does not fit with one or the other operating condition of the brake.
In the event that, additionally, an acceleration of the vehicle is detected or computed, there is another capability to check, in response to the acceleration, the plausibility of the signal currently generated by the pressure switch. Non-plausible is, for example, the display of an actuation of the brake although the vehicle significantly accelerates. An acceleration of the vehicle of at least approximately 0.2 g is deemed a significant acceleration.
Conversely, also a non-plausible signal is available if the pressure switch displays lack of brake pressure although the vehicle significantly decelerates, especially so if actuation of the brake is displayed on account of an electronic brake pressure regulation or a brake light switch. A significant deceleration in this respect is a deceleration that cannot be attained by the rear axle brake circuit alone so that it will have to be assumed that a brake pressure has been built up in the front axle brake circuit contrary to the signal generated by the pressure circuit which applies in the event of a deceleration from about 0.6 g onward.
With a defective condition of the pressure switch detected, it is advisable to activate an optical display, such as a pilot lamp.
Also, an emergency function of a brake slip control or of another electronic brake pressure control can be released. However, also in that case the driver should be warned as in an actual failure of the front axle brake circuit no additional detection of the defective condition will occur.
The pressure circuit arrangement according to the present invention is able to generate three different signals, depending on the operating condition of the pressure switch. A pulsated signal indicates a pressure built-up, a constantly high level is indicative of a non-pressurized brake circuit, while a constantly low level indicates a mass short circuit.
The invention will now be described more closely with reference to one form of embodiment in conjunction with the drawing.